Machinable plastic zinc alloy



Patented July 18, 1939 UNITED STATES PATENT OFFICE MACHINABLE PLASTIC ZINC ALLQY Arthur Burkhardt, Berlin-Lichterfelde, and Wolf gang Wolf, Magdeburg, Germany, assignors to Georg von Giesches Erben, Breslau, Germany, a corporation of Germany No Drawing. Application October 25, 1937, Se-

rial N o. 1937 4 Claims.

face finish is given to the work, but, above all,

that the chips'are short and spurting.

The only known non-ferrous alloy which posses'ses these properties is Ms 58, a brass containing 58 per cent copper, so-called automaticmachine brass.

It is an object of our invention to provide a substitute for Ms 58 which has similar properties.

To this end, we provide an alloy containing 2 to 5 per cent copper, 0.1 to 1 per cent bismuth, 0.1 to 1 percent manganese,- and fine zinc poor in iron and cadmium and practically free from magnesium and tin.

In the search for substitutes for Ms 58, it has been attempted to machine on automatic ma= chines ,zinc and aluminium alloys of the usual kind. This was a failure because the chips of such alloys are .curly and bulky and call themselves about the tool and the work.

An alloy which is to be a proper substitute for Ms 58 must deliver short and spurting chips on;

the same machines and underthe same cutting conditions as M5 58, and its finish must not be less perfectnor the life of the tool shorter.

Investigations showed that for obtaining short and spurting chipsfrom a zinc alloy, it is necessary to make additions which in liquid condition are only partly miscible with zinc.

Such-additions are lead, thallium, and bismuth. While they had a favorable influence on the formation of the chips, it was found that they were very detrimental with respect to intercrystalline corrosion. Thus, an addition of 0.1 per cent lead or bismuth to the well known die-casting alloy having 4 per cent aluminium, 3 per cent copper, 0.04 per cent magnesium, and zinc as the remainder, caused a growth of more than 7 per cent in length.

alloys free from aluminium and magnesium, with up to 5 per cent copper, and with addition of lead or bismuth do not suffer from intercrystalline corrosion and possess mechanical properties that they. can be used instead of Ms 58.

It was found, however, that the-percentage of lead must be 3 to 5 per cent in order to effect the desired formation of short, spurting chips, and

this has the drawback of greatly reducing the 170,855. In Germany The surprising discovery was made that zinc January 5,

ductility or the alloy so that it cannot be worked into bars or rods by extrusion.

Bismuth in amounts of 0.1 tol per cent is sufllcient for obtainingquite short chips and has a less detrimental influence on ductility, but ,still the plasticity and the mechanical properties of an alloy of copper and zinc with such percentages of bismuth are such that the alloy can be used in practice but still is not quite satisfactory.

We have made the surprising discovery that by' adding 0.1 to 1 per cent manganese to a bismuthcontaining copper-zinc alloy its plasticity and mechanical properties are improved, and the properties of its chips are not deteriorated.

The following table gives some examples of alloys embodying our invention.

In all alloys, the remainder or base is fine zinc poor in iron and cadmium and practically free from magnesium and tin.

Composition. in per cent Manga- Copper nese Bismuth Alloy (1) has given the best results with respect to working and to machining in an automatic a slight addition of aluminium, up to 0.15 per cent. This amount is not detrimental 'in other respects and the alloy can now be melted in an iron container.

We'claim: 1. A machin'able plastic zinc alloy containing from a small but effective amount up- 'to'5 per 1 cent of copper, from 0.'1 t0 v1 per cent ofv bismuth,

from 0.1 to 1 per cent of manganese, and time zinc poor in iron and cadmium, and practically tree from magnesium and tin, as the remainder.

2. A machinable plastic zinc alloy containing from 2 to 5 per cent of copper, from 0.1 to 1 per cent of bismuth, from 0.1 to 1 per cent of manganese, and fine zinc poor in iron and cadmium, and practically tree from magnesium and tin. as the remainder.

3. A machinable plastic zinc alloy containing from a small but efiective amount up to 5 per cent of copper, 0.1 to 1 per cent of bismuth, 0.1 to 1 per cent of manganese, the remainder substantially all zinc, and characterized by resistivity to producing short and Spurting chips when being machined.

ARTHUR BURKHARDT. WOLFGANG WOLF. 

